Geological Magazine

Original Article

Understanding the offshore flood basalt sequence using onshore volcanic facies analogues: an example from the Faroe–Shetland basin

DOUGAL A. JERRAMa1 c1, RICHARD T. SINGLEa1 p1, RICHARD W. HOBBSa1 and CATHERINE E. NELSONa1

a1 Department of Earth Sciences, The University of Durham, South Rd, Durham DH1 3LE, UK

Abstract

Flood basalts in associated volcanic rifted margins, such as the North Atlantic Igneous Province, have a significant component of lavas which are preserved in the present day in an offshore setting. A close inspection of the internal facies architecture of flood basalts onshore provides a framework to interpret the offshore sequences imaged by remote techniques such as reflection seismology. A geological interpretation of the offshore lava sequences in the Faroe–Shetland Basin, using constraints from onshore analogues such as the Faroe Islands, allows for the identification of a series of lava sequences which have characteristic properties so that they can be grouped. These are tabular simple flows, compound-braided flows, and sub-aqueously deposited hyaloclastite facies. The succession of volcanic rocks calculated in this study has a maximum thickness in excess of 6800 m. Down to the top of the sub-volcanic sediments, the offshore volcanic succession has a thickness of about 2700 m where it can be clearly identified across much of the area, with a further 2700 m or more of volcanic rock estimated from the combined gravity and seismic modelling to the north and west of the region. A large palaeo-waterbody is identified on the basis of a hyaloclastite front/apron consisting of a series of clinoforms prograding towards the eastern part of the basin. This body was > 500 m deep, must have been present at the onset of volcanism into this region, and parts of the water body would have been present during the continued stages of volcanism as indicated by the distribution of the hyaloclastite apron.

(Received April 21 2008)

(Accepted October 27 2008)

(Online publication February 26 2009)

Keywords:

  • British Tertiary;
  • LIP;
  • hyaloclastite;
  • lava sequences

Correspondence:

c1 Author for correspondence: D.A.Jerram@dur.ac.uk

p1 Present address: Senior Geologist, Det norske oljeselskap ASA, P.O. Box 2070 Vika, NO-0125 Oslo, Norway

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